Social Security Preservation Act of 2005 - Amends title II (Old Age, Survivors and Disability Insurance) (OASDI) of the Social Security Act to require the Managing Trustee of the Board of Trustees of the Federal Old-Age and Survivors Insurance Trust Fund and the Federal Disability Insurance Trust Fund (Social Security trust funds) to ensure that the annual surplus of the Social Security Trust Funds is invested in: (1) marketable interest-bearing obligations of the United States or obligations guaranteed by the United States; or (2) certificates of deposit in insured depository institutions. Prescribes a formula for determining the annual surplus of the Trust Funds.
Prohibits disinvestment of Social Security Trust Fund amounts from public debt obligations, any refraining from making such investments, or any delay in making normal deposits in such Trust Funds for public debt limit-related purposes. Authorizes the sale of Social Security Trust Fund public debt obligations, despite the public debt limit, for the payment of cash benefits and administrative expenses.